Over the last few decades revolutionary advances have been made in electrochemical storage and conversion devices expanding the capabilities of these systems in a variety of fields including portable electronic devices, air and space craft technologies, and biomedical instrumentation. Current state of the art electrochemical storage and conversion devices have designs and performance attributes that are specifically engineered to provide compatibility with a diverse range of application requirements and operating environments. For example, advanced electrochemical storage systems have been developed spanning the range from high energy density batteries exhibiting very low self discharge rates and high discharge reliability for implanted medical devices to inexpensive, light weight rechargeable batteries providing long runtimes for a wide range of portable electronic devices to high capacity batteries for military and aerospace applications capable of providing extremely high discharge rates over short time periods.
Despite the development and widespread adoption of this diverse suite of advanced electrochemical storage and conversion systems, significant pressure continues to stimulate research to expand the functionality of these systems, thereby enabling an even wider range of device applications. Large growth in the demand for high power portable electronic products, for example, has created enormous interest in developing safe, light weight primary and secondary batteries providing higher energy densities. In addition, the demand for miniaturization in the field of consumer electronics and instrumentation continues to stimulate research into novel design and material strategies for reducing the sizes, masses and form factors of high performance batteries. Further, continued development in the fields of electric vehicles and aerospace engineering has also created a need for mechanically robust, high reliability, high energy density and high power density batteries capable of good device performance in a useful range of operating environments.
Many recent advances in electrochemical storage and conversion technology are directly attributable to discovery and integration of new materials for battery components. Lithium battery technology, for example, continues to rapidly develop, at least in part, due to the discovery of novel electrode and electrolyte materials for these systems. From the pioneering discovery and optimization of intercalation host materials for positive electrodes, such as fluorinated carbon materials and nanostructured transition metal oxides, to the development of high performance non-aqueous electrolytes, the implementation of novel materials strategies for lithium battery systems have revolutionized their design and performance capabilities. Furthermore, development of intercalation host materials for negative electrodes has led to the discovery and commercial implementation of lithium ion based secondary batteries exhibiting high capacity, good stability and useful cycle life. As a result of these advances, lithium based battery technology is currently widely adopted for use in a range of important applications including primary and secondary electrochemical cells for portable electronic systems.
Commercial primary lithium battery systems typically utilize a lithium metal negative electrode for generating lithium ions which during discharge are transported through a liquid phase or solid phase electrolyte and undergo intercalation reaction at a positive electrode comprising an intercalation host material. Dual intercalation lithium ion secondary batteries have also been developed, wherein lithium metal is replaced with a lithium ion intercalation host material for the negative electrode, such as carbons (e.g., graphite, cokes etc.), metal oxides, metal nitrides and metal phosphides. Simultaneous lithium ion insertion and de-insertion reactions allow lithium ions to migrate between the positive and negative intercalation electrodes during discharge and charging. Incorporation of a lithium ion intercalation host material for the negative electrode has the significant advantage of avoiding the use of metallic lithium which is susceptible to safety problems upon recharging attributable to the highly reactive nature and non-epitaxial deposition properties of lithium.
The element lithium has a unique combination of properties that make it attractive for use in an electrochemical cell. First, it is the lightest metal in the periodic table having an atomic mass of 6.94 AMU. Second, lithium has a very low electrochemical oxidation/reduction potential (i.e., −3.045 V vs. NHE (normal hydrogen reference electrode). This unique combination of properties enables lithium based electrochemical cells to have very high specific capacities. Advances in materials strategies and electrochemical cell designs for lithium battery technology have realized electrochemical cells capable of providing useful device performance including: (i) high cell voltages (e.g. up to about 3.8 V), (ii) substantially constant (e.g., flat) discharge profiles, (iii) long shelf-life (e.g., up to 10 years), and (iv) compatibility with a range of operating temperatures (e.g., −20 to 60 degrees Celsius). As a result of these beneficial characteristics, primary lithium-batteries are widely used as power sources in a range of portable electronic devices and in other important device applications including, electronics, information technology, communication biomedical engineering, sensing, military, and lighting.
State of the art lithium ion secondary batteries provide excellent charge-discharge characteristics, and thus, have also been widely adopted as power sources in portable electronic devices, such as cellular telephones and portable computers. U.S. Pat. Nos. 6,852,446, 6,306,540, 6,489,055, and “Lithium Batteries Science and Technology” edited by Gholam-Abbas Nazri and Gianfranceo Pistoia, Kluer Academic Publishers, 2004, are directed to lithium and lithium ion battery systems which are hereby incorporated by reference in their entireties.
As noted above, lithium metal is extremely reactive, particularly with water and many organic solvents, and this attribute necessitates use of an intercalation host material for the negative electrode in secondary lithium based electrochemical cells. Substantial research in this field has resulted in a range of useful intercalation host materials for these systems, such as LiC6, LixSi, LixSn and Lix(CoSnTi). Use of an intercalation host material for the negative electrode, however, inevitably results in a cell voltage that is lower by an amount corresponding to the free energy of insertion/dissolution of lithium in the intercalation electrode. As a result, conventional state of the art dual intercalation lithium ion electrochemical cells are currently limited to providing average operating voltages less than or equal to about 4 Volts. This requirement on the composition of the negative electrode also results in substantial loss in the specific energies achievable in these systems. Further, incorporation of an intercalation host material for the negative electrode does not entirely eliminate safety risks. Charging these lithium ion battery systems, for example, must be carried out under very controlled conditions to avoid overcharging or heating that can result in decomposition of the positive electrode. Further, unwanted side reactions involving lithium ion can occur in these systems resulting in the formation of reactive metallic lithium that implicate significant safety concerns. During charging at high rates or at low temperatures, lithium deposition results in dendrides formation that may grow across the separator and cause an internal short-circuit within the cell, generating heat, pressure and possible fire from combustion of the organic electrolyte and reaction of metallic lithium with air oxygen and moisture.
Dual-carbon cells have also been developed that utilize lithium insertion reactions for electrochemical storage, wherein anions and cations generated by dissolution of an appropriate electrolyte salt provide the source of charge stored in the electrodes. During charging of these systems, cations of the electrolyte, such as lithium ion (Li+), undergo insertion reaction at a negative electrode comprising a carbonaceous cation host material, and anions of the electrolyte, such as PF6−, undergo insertion reaction at a positive electrode carbonaceous anion host material. During discharge, the insertion reactions are reversed resulting in release of cations and anions from positive and negative electrodes, respectively. State of the art dual-carbon cells are unable to provide energy densities as large as those provided by lithium ion cells, however, due to practical limitations on the salt concentrations obtainable in these systems. In addition, some dual-carbon cells are susceptible to significant losses in capacity after cycling due to stresses imparted by insertion and de-insertion of polyatomic anion charge carriers such as PF6−. Further, dual-carbon cells are limited with respect to the discharge and charging rates attainable, and many of these system utilize electrolytes comprises lithium salts, which can raise safety issues under some operating conditions. Dual carbon cells are described in U.S. Pat. Nos. 4,830,938; 4,865,931; 5,518,836; and 5,532,083, and in “Energy and Capacity Projections for Practical Dual-Graphite Cells”, J. R. Dahn and J. A. Seel, Journal of the Electrochemical Society, 147 (3) 899-901 (2000), which are hereby incorporated by reference to the extent not inconsistent with the present disclosure.
A battery consists of a positive electrode (cathode during discharge), a negative electrode (anode during discharge) and an electrolyte. The electrolyte contains ionic species that are the charge carriers. Electrolytes in batteries can be of several different types: (1) pure cation conductors (e.g., beta Alumina conducts with Na+ only); (2) pure anion conductors (e.g., high temperature ceramics conduct with O− or O2− anions only); and (3) mixed ionic conductors: (e.g., some Alkaline batteries use a KOH aqueous solution that conducts with both OH− and K+, whereas some lithium ion batteries use an organic solution of LiPF6 that conducts with both Li+ and PF6−). During charge and discharge electrodes exchange ions with electrolyte and electrons with an external circuit (a load or a charger).
There are two types of electrode reactions.
1. Cation based electrode reactions: In these reactions, the electrode captures or releases a cation Y+ from electrolyte and an electron from the external circuit:Electrode+Y++e−→Electrode(Y).Examples of cation based electrode reactions include: (i) carbon anode in a lithium ion battery: 6C+Li++e−→LiC6 (charge); (ii) lithium cobalt oxide cathode in a lithium ion battery: 2Li0.5CoO2+Li++e−→2LiCoO2 (discharge); (iii) Ni(OH)2 cathode in rechargeable alkaline batteries: Ni(OH)2→NiOOH+H++e− (charge); (iv) MnO2 in saline Zn/MnO2 primary batteries: MnO2+H++e−→HMnO2 (discharge).2. Anion based electrode reactions: In these reactions, the electrode captures or releases an anion X− from electrolyte and an electron from the external circuit:Electrode+X−→Electrode(X)+e−Examples of anion based electrode reactions include: (i) Cadmium anode in the Nickel-Cadmium alkaline battery: Cd(OH)2+2e−→Cd+2OH− (charge); and (ii) Magnesium alloy anode in the magnesium primary batteries: Mg+2OH−→Mg(OH)2+2e− (discharge).
Existing batteries are either of pure cation-type or mixed ion-type chemistries. To Applicants knowledge there are currently no known batteries having pure anion-type chemistry. Example of pure cation-type and mixed ion-type batteries are provided below:
1. Pure cation-type of battery: Lithium ion batteries are an example of pure cation-type chemistry. The electrode half reactions and cell reactions for lithium ion batteries are:
Carbon Anode:6C+Li++e−→LiC6 (charge)
Lithium Cobalt Oxide Cathode:2Li0.5CoO2+Li++e−→2LiCoO2 (discharge)
Cell Reaction:2LiCoO2+6C→2Li0.5CoO2+LiC6 (charge)2Li0.5CoO2+LiC6→2LiCoO2+6C (discharge)2. Mixed ion-type of battery: A Nickel/cadmium alkaline battery is an example of a mixed ion-type of battery. The electrode half reactions and cell reactions for a Nickel/cadmium alkaline battery are provided below:
Ni(OH)2 Cathode (Cation-Type):Ni(OH)2→NiOOH+H++e− (charge)
Cadmium Anode (Anion-Type):Cd(OH)2+2e−→Cd+2OH− (charge)
Cell Reaction:Cd(OH)2+2Ni(OH)2→Cd+2NiOOH+2H2O (charge)Cd+2NiOOH+2H2O→Cd(OH)2+2Ni(OH)2 (discharge)A Zn/MnO2 battery is an example of a mixed ion-type of battery. The electrode half reactions and cell reactions for a Zn/MnO2 battery are provided below:
Zn Anode (Anion-Type):Zn+2OH−→ZnO+H2O+2e− (discharge)
MnO2 Cathode (Cation-Type)MnO2+H++e−→HMnO2 (discharge)
Cell Reaction:Zn+2 MnO2+H2O→ZnO+2HMnO2 (discharge)
As will be clear from the foregoing, there exists a need in the art for secondary electrochemical cells for a range of important device application including the rapidly increasing demand for high performance portable electronics. Specifically, secondary electrochemical cells are needed that are capable of providing useful cell voltages, specific capacities and cycle life, while at the same time exhibiting good stability and safety. A need exists for alternative insertion/intercalation based electrochemical cells that eliminate or reduce safety issues inherent to the use of lithium in primary and secondary battery systems.